CN108219092B

CN108219092B - Preparation method of benzoxazine resin

Info

Publication number: CN108219092B
Application number: CN201810034218.7A
Authority: CN
Inventors: 田谋锋; 张力; 姚亚琳
Original assignee: Beijing Composite Material Co Ltd
Current assignee: Beijing Composite Material Co Ltd
Priority date: 2018-01-15
Filing date: 2018-01-15
Publication date: 2020-06-05
Anticipated expiration: 2038-01-15
Also published as: CN108219092A

Abstract

The invention discloses a preparation method of benzoxazine resin, which comprises the following steps: (1) uniformly mixing aniline and water at a first temperature of 20-30 ℃, and then adding monohydric phenol; the molar ratio of the monophenol to the aniline to the water is 1: 0.8-1.2: 5-10; (2) dripping a formaldehyde aqueous solution at a second temperature of 20-30 ℃; the molar ratio of the monophenol to the formaldehyde in the formaldehyde aqueous solution is 1: 1.5-2.5; the formaldehyde aqueous solution is dripped within 0.5-1 hour; (3) after the dropwise addition is finished, raising the temperature of the reaction system to a third temperature of 50-70 ℃, and preserving heat for 2-2.5 hours at the third temperature; (4) then, heating the temperature of the reaction body to the reflux temperature of the reaction system, and preserving the heat at the reflux temperature for 3-5 hours to finish the reaction; (5) and (4) decompressing and vacuum dehydrating until the reaction system is transparent to obtain the benzoxazine resin. The method is more suitable for industrial production.

Description

Preparation method of benzoxazine resin

Technical Field

The invention relates to a preparation method of benzoxazine resin, in particular to a preparation method of monoamine benzoxazine resin.

Background

Benzoxazine resin is a new type of high performance resin. The benzoxazine resin inherits the excellent thermal property, flame retardance and electrical insulation of the traditional phenolic resin and also has the following characteristics: no release of small molecules in the ring-opening polymerization process, almost zero curing shrinkage and flexible molecular design. Compared with the epoxy resin, the phenolic resin, the bismaleimide resin and other resins which are widely used at present, the benzoxazine resin has more outstanding comprehensive performance and is expected to be used as a flame retardant material in an aircraft cabin, a heat-proof and ablation-resistant material of a rocket engine and the like, so the benzoxazine resin has wide application prospect in the field of aerospace composite materials.

The synthetic method of the benzoxazine resin comprises a solution method, a melting method and a suspension method. The solution method has the advantages of simple and convenient operation, non-harsh reaction conditions, high yield and the like; but has the disadvantages of slow reaction rate, environmental pollution due to the need to use a large amount of organic solvent (e.g., toluene), and the like. In addition, residual organic solvents can interfere with the curing of the reaction product. The melting method has the advantages of short reaction time, few byproducts and the like, but has the defects of difficult temperature control, violent reaction, low ring formation rate and the like in synthesis. The suspension method has the advantages of low production cost, environmental protection, stable reaction and the like, but has the defects of low product purity, low yield and the like. For example, CN104356083A discloses a method for preparing benzoxazine compound by a suspension method, which uses water as a solvent, but needs an ice-water bath to control the temperature in the initial stage of the reaction, and is not easy to implement industrially and has high cost. In addition, cold water is required to be injected before discharging so that benzoxazine is solidified into brittle solid, and discharging is difficult in the middle and later stages of an industrial reaction kettle. Thus, the method is not easy to be industrialized.

Disclosure of Invention

The inventors of the present application have made intensive studies and have unexpectedly found that the step of controlling the temperature of an ice-water bath can be omitted by reducing the amount of water to be used and controlling the dropping speed of formaldehyde, and the step of injecting cold water can be omitted by vacuum dehydration, thereby completing the present invention. In view of the above, an object of the present invention is to provide a method for preparing benzoxazine resin, which is more suitable for industrial production. The technical scheme is adopted to achieve the purpose.

The invention provides a preparation method of benzoxazine resin, which comprises the following steps:

(1) uniformly mixing aniline and water at a first temperature of 20-30 ℃, and then adding monohydric phenol; wherein the molar ratio of the monophenol to the aniline to the water is 1: 0.8-1.2: 5-10;

(2) dripping a formaldehyde aqueous solution at a second temperature of 20-30 ℃; wherein the molar ratio of the monophenol to the formaldehyde in the formaldehyde aqueous solution is 1: 1.5-2.5; the formaldehyde aqueous solution is dripped within 0.5-1 hour;

(3) after the dropwise addition is finished, raising the temperature of the reaction system to a third temperature of 50-70 ℃, and preserving heat for 2-2.5 hours at the third temperature;

(4) then, heating the temperature of the reaction body to the reflux temperature of the reaction system, and preserving the heat at the reflux temperature for 3-5 hours to finish the reaction;

(5) and (4) decompressing and vacuum dehydrating until the reaction system is transparent to obtain the benzoxazine resin.

The invention greatly reduces the water consumption and controls the dripping speed of the formaldehyde aqueous solution, thereby omitting the step of controlling the temperature in the ice-water bath and being more suitable for industrial production.

In the present invention, the monohydric phenol represents a phenol having one hydroxyl group in the molecular structure. In step (1) of the present invention, the monohydric phenol may be selected from one or more of phenol, o-methylphenol, m-methylphenol, p-methylphenol, m-phenylphenol and p-phenylphenol. Preferably, the monohydric phenol is selected from phenol, m-methylphenol or m-phenylphenol. According to one embodiment of the present invention, the monohydric phenol is phenol. By using the monohydric phenol, ice water bath protection is not required.

In the step (1) of the present invention, the first temperature may be 20 to 30 ℃, preferably 22 to 25 ℃; the molar ratio of the monophenol to the aniline to the water may be 1:0.8 to 1.2:5 to 10, preferably 1:0.9 to 1.1:6 to 8. This is more favorable for the stability of the reaction system and the improvement of the yield.

In the step (2) of the present invention, the second temperature may be 20 to 30 ℃, preferably 22 to 25 ℃; the molar ratio of the monohydric phenol to the formaldehyde may be 1:1.5 to 2.5, preferably 1:1.8 to 2.3, for example 1: 2. This is more favorable for the stability of the reaction system and the improvement of the yield.

In the step (2), the concentration of the formaldehyde aqueous solution is 35-38 wt%. According to one embodiment of the invention, the concentration of the aqueous formaldehyde solution is 37% by weight. Commercially available aqueous formaldehyde solution products can be used.

In the step (2), the formaldehyde aqueous solution is added dropwise within 0.5 to 1 hour, preferably within 0.8 to 1 hour. By controlling the dripping speed, the side reaction can be effectively avoided, and the stability of the reaction system is ensured.

In the step (3) of the present invention, the third temperature may be 50 to 70 ℃, preferably 55 to 60 ℃; and preserving the heat for 2-2.5 h at the third temperature, preferably for 2-2.2 h. Suitable temperatures favor the reaction of monohydric phenol, aniline, phenol, but too high temperatures lead to side reactions. The reaction time cannot be too short, otherwise the reaction is insufficient; the reaction time is not suitable to be too long, otherwise side reactions can occur.

In the step (4), the temperature is maintained at the reflux temperature of the reaction system for 3 to 5 hours, preferably 3.5 to 4 hours. The reflux temperature of the reaction system means a temperature at which a reactant or a solvent of the reaction system is refluxed. At this temperature, the monohydric phenol, aniline, phenol continue to react. The reaction time cannot be too short, otherwise the reaction is insufficient; the reaction time is not suitable to be too long, otherwise the side reaction is aggravated.

In step (5) of the present invention, a process of injecting cold water into the reaction system so that the benzoxazine resin forms a brittle solid is not included. The invention obtains the product by vacuum dehydration instead of cold water injection. The vacuum dehydration product is a viscous liquid substance and is easy to discharge from the reaction kettle. If the brittle solid is obtained by adopting a cold water injection mode, the discharging from the reaction kettle is difficult or the discharging hole is blocked.

The preparation method of the invention omits the step of controlling the temperature by the ice water bath and the step of injecting cold water, thereby being more suitable for industrial production.

Drawings

FIG. 1 is an infrared spectrum of the product of example 1.

Detailed Description

The present invention will be further described with reference to the following specific examples, but the scope of the present invention is not limited thereto.

The test methods used in the examples and comparative examples are described below:

infrared spectrum: measured by an IRPrestige-21 infrared spectrometer from Shimadzu, Japan. Adopting KBr powder for tabletting and forming, mixing and grinding benzoxazine resin and KBr powder according to a certain proportion, and using stainless steel to press a film and tablet and form.

Example 1

1mol of aniline and 8mol of water are added to a 1000ml flask at a first temperature of 25 ℃, stirred homogeneously and 1mol of phenol are added. At a second temperature of 25 ℃, 37 wt% of formaldehyde aqueous solution (the amount of formaldehyde is 2mol) is added dropwise, and the dropwise addition is completed within 1 hour. And heating the reaction system to a third temperature of 60 ℃, and preserving the heat for 2 hours. And raising the temperature to the reflux temperature of the reaction system, and keeping the temperature for 4 hours to finish the reaction. And (4) decompressing, vacuum dehydrating until the reaction system is transparent to obtain a benzoxazine resin product. The IR spectrum of the product is shown in FIG. 1. The product yields are given in table 1.

Examples 2 to 3 and comparative example 1

The reaction materials were adjusted as shown in Table 1, and the other conditions were the same as in example 1. The product yields are given in table 1.

TABLE 1

Numbering	Example 1	Example 2	Example 3	Comparative example 1
					Aniline (mol)	1	1	1	1
Water (mol)	8	8	6	88
					Monohydric phenol	Phenol and its preparation	Meta-methylphenol	Phenol and its preparation	Phenol and its preparation
Monohydric phenol (mol)	1	1	1	1
					Formaldehyde (mol)	2	2	2	2.2
Yield (%)	96	95	97	87

Comparative example 2

A benzoxazine resin was prepared according to example 4 of CN 104356083A. An ice water bath was required to control the temperature and a brittle solid was obtained by injecting cold water in 87% yield.

The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.

Claims

1. The preparation method of the benzoxazine resin is characterized by comprising the following steps:

(1) uniformly mixing aniline and water at a first temperature of 20-30 ℃, and then adding monohydric phenol; wherein the molar ratio of the monohydric phenol to the aniline to the water is 1: 0.9-1.1: 6-8; the monohydric phenol is phenol, m-methylphenol or m-phenylphenol;

(3) after the dropwise addition is finished, raising the temperature of the reaction system to 55-60 ℃ at a third temperature, and preserving heat for 2-2.2 hours at the third temperature;

(4) then, heating the temperature of the reaction body to the reflux temperature of the reaction system, and preserving the heat at the reflux temperature for 3.5-4 hours to finish the reaction;

(5) decompressing and vacuum dehydrating until the reaction system is transparent to obtain benzoxazine resin; this step does not include a process of injecting cold water into the reaction system so that the benzoxazine resin forms a brittle solid.

2. The method according to claim 1, wherein the first temperature is 22 to 25 ℃ in the step (1).

3. The method according to claim 2, wherein in the step (2), the second temperature is 22 to 25 ℃ and the molar ratio of the monohydric phenol to the formaldehyde is 1:1.8 to 2.3.

4. The method according to claim 3, wherein the concentration of the aqueous formaldehyde solution in the step (2) is 35 to 38 wt%.

5. The method according to claim 4, wherein the step (2) comprises adding the aqueous formaldehyde solution dropwise within 0.8 to 1 hour.